The development of the adrenal medulla is accompanied by marked alterations in the levels of catecholamines and catecholamine synthesizing enzymes as well as changes in the uptake and storage of amines; these changes are due in part to changes in the level of neural stimulation of the gland. Reserpine alters both the uptake and synthesis of catecholamines, by inhibiting ATP-Mg 2 ion stimulated uptake in storage vesicles and by reflex stimulation resulting in transsynaptic induction of tyrosine hydroxylase and dopamine beta- hydroxylase; thus, the character and intensity of the effects of reserpine may be age-dependent and reserpine may alter the development of adrenal amine stores. The age-dependence of specificity and sensitivity to reserpine blockade of uptake will be measured in vitro using isolated adrenal storage vesicles incubated with C14-epinephrine or H3-metaraminol. Additionally, after administration of reserpine to developing rats, the levels of catecholamines, tyrosine hydroxylase and dopamine beta-hydroxylase will be assayed to determine direct and reflexly mediated effects. In some experiments, chlorisondamine will be given to prevent reflex neural stimulation from reserpine; this will enable differentiation of direct and reflex effects. These data can provide valuable information on the short and long-term effects of reserpine in neonates.